After completion of decoding of the human genome sequence, attention has been drawn to proteome analysis in which proteins in actual charge of life phenomena are analyzed. This is because the direct analysis of a protein probably leads to the determination of the cause of disease, the development of new drugs, and tailor-made medicine. For example, a specific polypeptide called a marker protein is known to be selectively expressed on a certain type of diseased cells; the detection of the marker protein with high sensitivity is an important technology leading to the early detection of disease or the like.
Other reasons why the proteome analysis has received attention include the facts that the expression of a protein has proved to be incapable of being well predicted by the expression analysis of RNA as a transcript, i.e. transcriptome analysis, and that it is difficult to obtain the modified site and three-dimensional structure of a protein modified after translation from genomic information.
Mass spectrometry is widely used for proteome analysis because it can measure a polypeptide with high sensitivity and high resolution. Particularly, a matrix assisted laser desorption/ionization mass spectrometry method (MALDI-MS) can detect a peptide with a high mass number and hence is effectively used.
In recent years, attention has been given to measurement using a secondary ion mass spectrometry method (SIMS), which is a mass spectrometry method having high spatial resolution and reproducibility.